This invention relates to an apparatus for automatically grasping the leading end of a fiber web to start sliver formation therefrom. The apparatus is used, for example, in a carding machine in which the fiber web obtained from a roller assembly of the card is at least in part gathered and further advanced by a web transporting device, and in the starting phase the non-utilizable fiber web length is admitted to a web delivery device and is subsequently removed therefrom. In the thread-in phase the useful fiber web is surrounded by a trumpet and shaped into a sliver and further, the sliver discharged by the trumpet is advanced to a calender roll pair.
In practice, prior to the thread-in, the non-utilizable fiber web obtained, for example, from the crushing rolls is in a first step (starting phase) gathered by hand and thereafter torn off and removed. In a second phase (thread-in and production phases) the useful fiber web which is also discharged by the roll assembly of the card is gathered manually and thereafter, it is manually tapered and threaded through a trumpet into the gap formed by a calender roll pair which grasps the sliver and advances it to a sliver coiler which, in turn, deposits the sliver into a coiler can.
Published European Patent Application 314,310 discloses a method according to which the fiber web is gathered by two take-off belts and is compressed to a pre-sliver and further transported by two transfer or conveying rolls. During this phase of operation, a two-part segmented trumpet is in its open position so that the pre-sliver is not contacted by the trumpet. Also during this phase, the transfer rolls are driven with a first speed which is two to three times greater than the circumferential speed of the take-off belts, whereby a removal of fibers from the pre-sliver occurs. This results in a significant stretch of the fibers between the transporting rolls of the take-off belts and the transfer rolls, whereby the non-utilizable fiber parts of the pre-sliver are, in the starting phase, separated and removed.
The transfer rolls tear large tufts or clumps from the pre-sliver which fall into a suction pipe and are removed as waste. The tearing of fiber parts from the pre-sliver results in a generally tapered leading or threading end for the pre-sliver. The tapered pre-sliver terminus is introduced downwardly into the V-shaped structure of an air trumpet.
After completion of the starting phase (first step), the speed of the transfer rolls is reduced to a second, normal speed so that the circumferential speed thereof corresponds to that of the take-off belts. After the starting phase the thread-in procedure (second step) is effected upon introduction of the tapered pre-sliver into the air trumpet. From the air trumpet a tapered sliver emerges which, in turn, enters into the gap between a groove-and-feather roll pair and subsequently the sliver is deposited in the coiler can. As the carding machine has attained its normal production speed, in a third step the two parts of the segmented trumpet are brought together to thus place the trumpet in a closed position in order to surround the pre-sliver for preventing an expansion thereof over the surface of the transfer rolls. Stated differently, the segmented trumpet participates neither in the sliver formation nor in the tapering procedure of the fiber sliver.
It is a disadvantage of the above-outlined process that the terminus of the pre-sliver may rupture completely when large tufts or clumps are torn therefrom, causing the flow of fiber material to be interrupted, and thus an introduction of the pre-sliver into the fast-rotating transfer rolls cannot be effected in a satisfactory manner. Further, an undesired settling or clogging may occur. It is a further significant disadvantage of the above-outlined arrangement that the sliver formation is effected by pneumatic forces in the air trumpet. Such an arrangement is significantly complex and expensive and, particularly in case of errant air streams, leads to operational disturbances and consequently, a fully automatic thread-in is not possible.